1. Field of the Invention
The invention relates to a high frequency (HF) sealing strip for electro-magnetically shielded, insertable electronic modules, said sealing strip comprising a core of at least partially elastically deformable material, a cover of a flexible and conductive material, in particular a non-woven material or textile fabric, which encloses the core and establishes an electrical connection between adjacent electronic modules and/or between a chassis for accommodating the electronic modules and an electronic module, as well as a contact surface formed by a section of the cover.
2. Related Art
Electronic devices configured with a modular-unit design consist of individual plug-in components or electronic modules, which are inserted into a sub-rack or chassis. The individual electronic modules are embodied such that they can be inserted or pulled out to facilitate the installation and/or or replacement, wherein these modules are inserted and removed in a direction perpendicular to the front of the electronic module, in depth direction. The modules are guided on the side by guide rails installed in the sub-rack and/or chassis.
When fully inserted, the front panel of the electronic module closes off the front of the sub-rack or chassis. The front panel frequently has a U-shaped cross section, with two side legs extending at a right angle from the front panel toward the back and toward the inside of the chassis or sub-rack. These legs extending toward the back function as contact surfaces for establishing an electrically conductive connection to the adjacent electronic modules or other chassis parts, thereby providing a good shielding to prevent high-frequency electromagnetic radiation (HF radiation) from entering and/or exiting. In some cases, the front panels are provided with legs angled toward the back along all four edges.
Special contacting elements are used to provide a tight HF seal for the unavoidable gaps between adjacent electronic modules. These special contacting elements can take the form of metal contact strips with spring elements or compressible seals of a conductive textile material.
Soft HF sealing strips of textile material have several advantages: They can be installed simply by attaching them to a level sealing surface, for example with the aid of adhesive tape sections, without having to use tools or any special skills. Endless webs of textile material can be produced relatively cheaply and can be cut on location into strips of a desired length. As compared to sharp-edged spring elements, textile seals are easy to handle and cannot cause injuries to persons or damage to the mechanical and electronic components.
Electro Magnetic Compatibility (EMC) profile seals with a core of foam material and a textile cover coated with a copper-nickel coating are known. These profile seals have a level contact surface for attaching them to a front panel and a curving bulge that projects away from the contact surface.
FIG. 6 in reference EP 1 052 887 A2 discloses a sealing strip, comprising a foam material core and a cover of a conductive fabric. In the region of one edge, the fabric for the cover forms a flap with an essentially U-shaped cross section. The foam material core is relatively thick as compared to the thickness of the cover fabric, even in the edge region.
The textile seal, Series 7000 Profile 74095, marketed by the company Chomerics, also comprises a foam core surrounded by a cover of a polyester material with nickel-copper coating. The elastically deformable foam core decreases in size toward the edges of the seal while the edges themselves are slightly rounded.
This known profile seal has a symmetrical cross section resembling a sinusoidal wave, wherein the thickness of the seal exceeds 1mm in the edge region already, with a total thickness of 3 mm.
As long as textile material seals are pressed only perpendicular against the surface to which they must adhere, they meet all requirements of a good and permanent HF seal. The problem arises when they are stressed by shearing forces acting in transverse direction upon the seal, meaning parallel to the gluing surface. If textile sealing strips are used between opposite-arranged sides of adjacent electronic modules, which can be inserted and pulled out, the danger exists that the resilient sealing strips are peeled off the adhering surface, in particular during the insertion of the modules, or that the sealing bulges are deformed excessively. Above all, cut edges of front panels or sharp corners can quickly damage or totally destroy sealing strips of textile material or can tear these off the background.
In recent years, demands have been voice for particularly thin textile seals which can be stressed by shearing forces acting parallel to the adhering surface. For example, the AMC standard (advanced mezzanine card specification) developed by the PICMG (PCI Industrial Computing Manufacture Group) for telecommunication applications requires a HF seal with a thickness only marginally above 2 mm in the non-stressed state.